feat(spinner): update --color to be internal

Author: thetaPC

core/src/components/spinner/spinner.scss

@@ -5,10 +5,13 @@
 // --------------------------------------------------
 
 :host {
+  // This variable controls the component's color when nested within parent elements (e.g., `ion-button`). It is intended for internal styling only.
+  --color: var(--ion-spinner-color);
+
   display: inline-block;
   position: relative;
 
-  color: var(--ion-spinner-color);
+  color: var(--color);
 
   user-select: none;
 }